1. Field of the Invention
This invention relates to an image forming apparatus, such as a copier, a printer or the like which uses an electrophotographic method, an electrostatic recording method or the like, and to a method for controlling such an apparatus.
2. Description of the Related Art
In image forming apparatuses which use an electrophotographic method, an electrostatic recording method or the like, an approach for improving the stability of image quality by forming a specific pattern on an image bearing member, reading the density of the formed pattern, and correcting the density and gradation of the pattern is known. In another approach for improving the stability of image quality, a specific pattern is formed on a recording material, the density of the formed pattern is read, and the density and gradation of the formed pattern is corrected.
However, it is difficult to satisfactorily correct and control both short-term changes in the reproducibility of the density and gradation of the obtained image caused, for example, by changes in environment, and long-term changes in the reproducibility of the density and gradation of the obtained image caused, for example, by changes in the properties of the photosensitive member and the developer during the use of a long time period, only according to the above-described correction methods.
In order to solve the above-described problems, the assignee of the present application has provided proposals in U.S. Pat. No. 5,583,644 and U.S. Ser. No. 409,811 (filed Mar. 24, 1995). However, there is still room for improvement in dealing with short-term changes in the reproducibility of the density and gradation of the obtained image.